Chevy Small Block Dyno Tests - Old School Meets New

406ci Traditional Mouse Vs. Late-Model 402ci LS2

We initially tossed the idea of comparing a stock LS1 with a conventional small-block 350, but after questioning the angle we later realized, what's the fun in that? And dare we say, it's already been done by others who'll be the first to admit that they did a fair job of updating you with the crucial differences--but certainly did little to stimulate the gearhead factor. To kick it up a notch, and satiate our hunger for power, we set the stage to bump up the cubic inches of a later-model LS2 into a big-inch 402 and pin it against a "warmed over" 406ci small-block.

Our requirements for this challenge: All components had to be readily available, over-the-counter production pieces; nothing over 11:1 compression; we had to use a hydraulic-roller camshaft; and we had to keep the components as close as possible, meaning we had to use the same manufacturer for our cylinder heads, camshafts, and manifolds, and most importantly, both bullets had to share the same carburetor.

Doesn't seem like that big a deal, right? Wrong. You need to take a closer look at the flow capacity of an LS cylinder head. Given the nature of its 15-degee valve angle over the conventional 23-degree cylinder head, we're talking race technology that's trickled down to the consumer level. By altering the angle of the valve, you create a much more direct path, which allows a greater volume of air to traverse into the combustion chamber at a faster rate. The result is radical flow numbers that help to create big horsepower. As you can imagine, the obvious advantage already went to the LS before we even began building the engines.

The real question becomes, was either engine significantly cheaper or did one walk away as the clear winner? Follow along, and you be the judge. Don't forget to write in to us at chevyhi@ primedia.com and let us know what you think of the results.

Inside is a complete Lunati LS1 Pro Series stroker kit assembly featuring a 4340 forged crankshaft with a 4-inch stroke, 4340E billet rods, forged pistons, and main bearings. Yeah, this baby isn't going to break anytime soon, and the added rigidity will allow for aggressive testing in upcoming issues. One thing we need to note is that the crankshaft featured a 24-tooth reluctor wheel, which was swapped for a 58-tooth wheel to work with the Edelbrock controller.

Like the LS1/LS6 and LQ9 blocks, the LS2 features a six-bolt main. The inner bolts were torqued to 58 ft-lb, 55 ft-lb for the outer, and 25 ft-lb for the cross-bolts.

One of the biggest advantages of the LS engine is having the ability to swap camshafts with minimal effort. All you have to do is remove the front timing cover, loosen the rocker arms, and slide two rods to support the lifters. Keeping that in mind, we started small with the 230/232 duration at 0.050 (PN XER281HR) and later stepped up to a larger 238/240 duration stick (PN XER287HR).

To help keep the timing in check, we used a Motion double-roller timing chain. The raised ridge is where the cam sensor takes its reading.

Head gasket of choice was a factory 6.0L steel gasket that measured 0.057 inch compressed, giving us 11:1 compression with the 62cc-chamber Dart 225s.

Rather than using the factory lifters, we went with Comp Cams Pro Magnum hydraulic-roller lifters, specifically designed for high-rpm floggings.

Unlike the LS1/LS6 and the LQ9 block, there are no bosses for the dual knock sensors in the valley pan; instead they're placed on the side of the block. Also, if you're using an older LS1/LS6 processor, be sure to use the correct knock sensors, as the LS2 knock sensors feature a two-wire design over the previous one-wire setup and are incompatible with the LS2 processor.

Moving the air is a set of Dart Pro 1 LS1 cylinder heads. Cast out of 355-T6 aerospace alloy, they feature 2.05-/1.60-inch intake/exhaust valves and a 225cc runner volume (205s are also available) and can flow as much as 313 cfm on the intake port and 214 cfm on the exhaust at 0.600 inch lift.

While the ports are as cast from Dart, the combustion chambers are bowl-blended on a five-axis CNC machine and available in a 62cc configuration.

While the ports are as cast from Dart, the combustion chambers are bowl-blended on a five-axis CNC machine and available in a 62cc configuration.

An added bonus to the Lunati stroker kit is that everything comes balanced and ready to be assembled. Included are plasma-moly file fit rings with billet rods measuring 6.125 inches in length.

Since the intake rocker-arm stud extends through the port, it's a good idea to use sealant to prevent any oil from seeping in. To keep the head mated to the block, we used a complete set of ARP head studs. The smaller upper bolts were torqued to 23 ft-lb while the larger bolts were set at 70.

Completing the valvetrain, we used a set of Comp Cams 1.75:1 roller rockers with a 3⁄8-inch stud.

Expect to dab a little sealant on the four corners of the front and rear cover prior to mounting the oil pan. It's also important to note that on any stroker combination, you'll need to place a washer, measuring 0.110 inch, underneath the windage tray to prevent the crank from rubbing into it.

Again, even with the manifold, there's no sealant here. Simply press in the factory rubber O-rings. If you can't get them through your local GM dealer, Turn Key can take care of your needs.

The end product is eye-fetching, isn't it? While we chose to utilize Westech's MSD coil packs and wires, you can shave off $680 if you have access to the factory pieces; however, you should be aware that the MSD unit is designed to work with the factory electronics and will be offering a programmer to control every aspect of ignition timing.

We gained an additional 5 hp by using a 1-inch tapered four-hole Super Sucker spacer from High Velocity Heads, netting us the final 583hp figure.

If you plan to use an LS2 block like we did with the LS1 Edelbrock manifold and controller, be advised that you'll need to do a slight modification. The LS2 uses a 5-volt cam sensor, whereas the LS1/LS6 and LQ9 use a 12-volt cam sensor. Since the controller was originally designed to read the 12-volt sensor, you'll need to reverse the two outer wires to change the polarity. This works well, but by the time you read this, it'll already have been addressed.

The basis for our Gen I challenger was a well-seasoned 400 small-block core, which Coast High Performance clearanced for a 4340 forged-steel crank working 6-inch rods through a 3.750-inch stroke--a combination Coast High calls its 406ci Pro Mod short-block.

You've noted that our 400 uses two-bolt mains. Our engine builder, Jun Nakawatase, pointed out that four-bolt-main 400s are actually weaker than their two-bolt brethren, since the extra bolt runs through the thinnest part of the cap and the block casting. We used ARP main studs for maximum strength.

To achieve the compression we were looking for, the block was decked 0.0020 inch and flat-top pistons were used to create a zero piston deck height. We came in a smidgen above the limit at 11.1:1. Nakawatase used a bit of racer savvy to maximize the potential of our 406, deburring the sharp edges on the pistons to help minimize hot spots, and thereby detonation. Did it work? Given that our optimum total timing was 39 degrees, we'd say it didn't hurt.

To achieve the compression we were looking for, the block was decked 0.0020 inch and flat-top pistons were used to create a zero piston deck height. We came in a smidgen above the limit at 11.1:1. Nakawatase used a bit of racer savvy to maximize the potential of our 406, deburring the sharp edges on the pistons to help minimize hot spots, and thereby detonation. Did it work? Given that our optimum total timing was 39 degrees, we'd say it didn't hurt.

We knew we'd have to move massive quantities of air to match up with our Gen IV opponent, so we reached right for Dart's top shelf, choosing a set of Pro I 227 CNC cylinder heads. These gorilla lungs are cast of 355-T6 aluminum alloy and run 2.08/1.60-inch intake/exhaust valves. The valves are controlled by 1.550-inch springs, which are held in place by 10-degree titanium retainers.

The intake ports of the Pro I CNC heads are thoroughly massaged, measuring 227cc and moving 302 cfm at 0.600 inch lift. Our stout cam, when combined with 1.6:1 rockers, works 0.600/0.619 inch lift and 248/254 degrees duration at 0.050--an ideal match for these heavy-breathing heads.

Of course, our primary motivation for choosing the Pro 1 CNC heads is the fact that they're fully ported. The port volume on the worked-over exhaust side comes in at 85 cc, which is a full 10 cc over the regular Pro 1 head. This side flows 220 cfm at 0.600 inch lift, which combined with our cam to move burnt gases out quickly and efficiently.

Unsure of what the future would hold for our 406 creation, Coast High went ahead and drilled the steam passages in our heads. This is definitely a "measure twice, drill once" type of task.

Speaking again of fully ported, the Pro 1 227 CNC heads also feature a thoroughly worked-over and bowl-blended combustion chamber. Once the machines have had their way with the castings, the chambers each measure 66 cc--not the more commonly seen 64 cc. It makes a difference when calculating compression ratio.

The extensive Fel-Pro gasket kit we used included top-grade MLS (multilayered steel) head gaskets. Compressed thickness measures 0.041 inch. The gasket edges don't reach all the way to the intake valley, so a little bit of sealant is needed (arrow).

After consulting with ARP, we used 12-point Pro Series head bolts. These fasteners are rated at 200,000 psi, the same as ARP's head studs, giving us better-than-average strength, to say the least. As is standard we used ARP's moly lube on the bolt heads and thread sealant on the appropriate area, which passes though the coolant passages.

Continuing our quest for as much valvetrain stability as possible, Coast High installed a set of its prototype shaft-mount 1.6:1 offset rocker arms atop our Pro 1 heads. (They'll be in regular production by the time you're reading this.)

We outfitted the front end of our stroker crank with a Rattler torsional vibration absorber. Also note our one-piece oil gasket. Our block required a piece with a thick front seal (PN 1880), marking it as a '75-and-later small-block timing cover. Note that it also provides clearance for our stroker crank setup.

In the name of achieving every last pony possible, we took note that the Dart Pro 1 227 CNC heads are gasket matched to Fel-Pro 1206 intake gaskets...

...and so is the port-matched version of Edelbrock's ubiquitous Victor Jr. manifold. This CNC gasket-matched intake is an off-the-shelf part, so we went for it. When it comes to intake flow, every little bit counts, right?

All that remained was for Nakawatase to bolt the Victor Jr. into place, then take a moment to admire his handiwork before loading this contestant into the truck and heading off to the dyno. If you look closely, you'll note that Nakawatase fitted our ARP intake bolts with larger-than-normal washers, a step he always takes with slotted intake manifold bolt holes.

On the scene at Westech, Steve Brulee quickly set up our MSD Pro-Billet distributor. Brelee installed the largest advance stop bushing, limiting centrifugal advance to 18 degrees. He also installed one silver and one blue advance spring, ensuring all our timing would be in by approximately 2,800 rpm.

All that work led us to this point, on the dyno in our 406's best fighting trim--and this thing is a fighter. We achieved max power with a 76/83 jet combo in the 750-cfm Mighty Demon mixer both engines used; in other words, our powerplant needed the four jet sizes Brulee removed for the Gen IV runs. It looks cool, sounds nasty, and makes as much power as its 402ci opponent, which gave us just about everything we could want.